One of the major problems in development and aging is that we do not understand the nature of the "developmental program" through which a cell passes between birth and death. Insect metamorphosis involves a conspicuous program with many advantages for analysis. We have developed culture conditions which permit lepidopteran pupal wings to form adult cuticles after ecdysone stimulation and pupal cuticles when juvenile hormone is present. We plan to determine when pupal and adult cuticular proteins first appear in the cultures and define the critical period of juvenile hormone's action. Further dissection of the control of the program will involve comparisons of the action of juvenile hormone, inhibitors of transcription and RNA processing, and high levels of ecdysone on the synthesis of specific cuticular proteins.